348 The Nerves and Muscles of the Leg 
peroneus profundus. One of these runs to the muscle near its upper 
extremity and passes distally across the central third of the obliquely 
placed fibre bundles of the proximal portion of the muscle. The other 
branch leaves the n. peroneus profundus more distally, extends to the 
middle or lower third of the muscle and then distally across the middle 
third of the obliquely placed fibre bundles of the lower portion of the 
muscle and across the corresponding fibre bundles of the m. peroneus 
tertius. 'The two nerves may be bound up in one trunk or their place 
may be taken by a considerable number of branches, but in 9 cases out 
of 10 essentially the arrangement described may be found. 
The extensor digitorum longus and extensor hallucis longus are represented 
in urodeles by the femoro-fibule-digiti I-V which extends from the lateral 
epicondyle of the femur and from the fibula to the foot and thence by means 
of tendinous processes to the phalanges (Hoffmann). In reptiles the two 
muscles are probably also represented by the extensor digitorum longus 
which in most reptiles arises from the lateral epi-condyle of the femur and 
is inserted by tendinous slips into the bases of some of the metatarsals. In 
chelonians it is inserted by tendons into the phalanges (Gadow, 82). In 
the mammals the extensor digitorum and extensor hallucis are distinct in 
most forms. The extensor digitorum arises chiefly from the proximal part 
of the tibia and is united to the back of the toes by tendinous process which 
vary considerably in different forms (Ruge, 78). In man doubling of the 
digital tendons and aberrant tendon slips are very frequent (Le Double). 
Early in embryonic development, as we have seen above. the tendons are 
represented by a tendon plate. In the adult the tendons may be connected 
by an uninterrupted aponeurotic lamella or by tendinous slips, conditions 
normal in many of the lower mammals. Occasionally in man slips from the 
tendons of the long digital extensor pass to the first, fourth, or fifth meta- 
tarsals (Testut). This corresponds to the attachment of the extensor ten- 
dons to the metacarpals found in reptiles. In the human embryo the 
extensor tendon plate is at first connected with the metatarsal scleroblastema 
but is gradually separated from this as development proceeds. 
M. peroneus tertius.—Schomburg, oo, finds this muscle distinct from 
the extensor digitorum pedis longus even in the sixth week. In the two 
embryos in which I have made the most careful study of these muscles 
(144, length 14 mm., Plate IX, Fig. 1; and 22, length 20. mm., Plate 
IX, Fig. 2) I have been unable to find a sharp distinction between the 
two muscles, although the tendon of the peroneus tertius in embryo 22 
is quite distinct from that of the extensor digitorum longus. Schomburg 
finds the tendon of the m. peroneus tertius runs at first toward the third 
“It is possible that the m. extensor hallucis proprius of reptiles is homo- 
logous with the extensor hallucis longus of mammals. It seems more likely 
that it should be classed with the dorsal pedal muscles. 
